The present invention relates to a ratio control system for a continuously variable transmission in a motor vehicle.
U.S. Pat. No. 4,735,113 discloses a continuously variable transmission for a vehicle. According to a known ratio control system for the continuously variable transmission, a feedback control is effected whereby a reduction ratio in the continuously variable transmission is controlled in such a direction as to decrease an input revolution speed error or deviation toward zero. In this known feedback control, proportional and integral gains are constant. If such feedback gains are set so as to effect an optimum upshift toward the smallest or minimum reduction ratio during operation with large throttle openings, an excessively quick upshift results during operation with small throttle openings. On the contrary, if the gains are set so as to effect an optimum upshift during operation with small throttle openings, an excessively slow upshift results during operation with large throttle openings. Thus, a difficulty arises in setting the feedback gains.